A. Field of the invention
The present invention relates to a bicycle, and more particularly to a drive mechanism on a bicycle for transmitting power to the rear wheel.
B. Description of the related art
In general, a bicycle includes a frame, a front fork, a steering portion, a front and rear wheel, and a drive portion for rotating the rear wheel. The drive portion includes a chain wheel and a crank rotatably supported on the frame, a sprocket mounted on the rear wheel, and a chain extending between the chain wheel and the sprocket. The number of teeth on the chain wheel is larger than that on the sprocket, thereby rotating the rear wheel faster than the chain wheel.
Because power is transmitted directly from the chain wheel to the sprocket on the rear wheel via the chain, the chain wheel must be much larger than the sprocket. However, because the rotational axis of the chain wheel and the rotational axis of the rear wheel are generally the same height above the ground, there is relatively little clearance between the ground and the bottom of the chain wheel.
In addition, on some bicycles a chain cover is mounted around the chain in order to help prevent the rider's clothes from being soiled or entangled by the drive portion. However, because the chain cover is a separate part, the number of the parts of the bicycle is increased, thus requiring addition work during assembly. In addition, a chain cover that completely surrounds the chain would further reduce the clearance between the bottom of the chain wheel and the ground.